1. Field of the Invention
This invention generally relates to devices for blocking the flow of traffic along a traffic pathway and more specifically to gates that control automotive flow at a highway railroad crossing.
2. Description of Related Art
Efforts are being made to improve safety at railroad gate crossings. The purpose is to prevent collisions between trains and automotive vehicles. Conventional crossing gates comprise two crossing gate assemblies. One gate is positioned on each side of the railroad crossing. When the gate is in a blocking position it blocks only the approach lane or lanes of a highway, not the exit lanes. So it is possible for a person to cross the tracks with the gates in their blocking positions.
More recently it has been suggested to use four crossing gates. A pair of gates are positioned on each side of the highway. One gate closes the approach lane and the other the exit lane. As a result the gates on the opposite sides of the highway provide a substantially continuous barrier. This approach is effective, but it also is expensive because it requires twice the number of gates with all their structures and costs and twice the maintenance. Further, upgrading existing crossings still require a significant effort in routing utilities either across the highway or beneath the tracks in order to control the operation of the two additional gates. Consequently many railroad crossings continue to be guarded by two gates that only block the approach lanes.
Other approaches for improving railroad crossing gates have been suggested. One initially obvious and simple approach would appear to be merely extending the length of the crossing gate so it extends completely across a highway in a blocking position. In many situations, however, this is not possible because the position of the gate in an open, or vertical, position may interfere with trees, power lines or other structures proximate the crossing gate location. Moreover, such an elongated gate must be constructed with sufficient strength to withstand environmental and other factors.
It has been proposed to use “extendible” gates. An extendible gate generally has a rotatable arm that swings between open and blocking positions and that carries an extendible member. Some operating mechanism extends and retracts the member as the rotatable arm moves between blocking and open positions. U.S. Pat. No. 441,226 depicts one such extendible gate in which a first section can tilt freely from a vertical, or open, position to a horizontal, or blocking, position and carries a movable section. The operating mechanism comprises a ramp or inclined way frame and a pendulum-like device. The pendulum-like-device includes a wheel that rides on the way frame and a weighted rod that engages the movable section. When the first section tilts to a blocking position, the wheel and rod move down the ramp and extend the arm.
In U.S. Pat. No. 494,390 the operating mechanism comprises a pulley that connects to a swing arm proximate a base. The pulley has a pinion attached to a fixed segment gear. An endless band connects to an inner end of an extendible arm and wraps around the pulley. As the swinging arm rotates, the pulley rotates relative to the swing arm, and the cable extends or retracts the extendible arm.
U.S. Pat. No. 4,666,108 discloses a railroad crossing gate with a first rotatable member that carries a telescoping member. However, the extension merely allows adjustment of the overall length of the crossing gate to be determined at an installation site. The telescoping member does not move relative to the first rotatable member after installation.
U.S. Pat. No. 6,212,825 is an example of a gate with a motor driven operating mechanism. The mechanism rotates the secondary gate between extended and retracted positions with respect to a primary gate. The motor drive attaches to the free end of the primary gate.
U.S. Pat. Nos. 6,618,993 and 6,267,332 depict railroad grade crossing systems in which a motor drives an extendible member between extended and retracted positions for purposes of completely closing vehicle access to a railroad crossing.
The foregoing patents disclose operating mechanisms of different implementations. However, they all require increased maintenance. Each operating mechanism is subject to wear and vandalism. The motor-driven railroad crossing gates are more expensive to manufacture and still require further maintenance.
In addition, it is estimated that there are many thousands of railroad grade crossings that need to be upgraded allowing a single crossing gate to block both the approach and exit lanes of one side of the grade crossing. It might appear that these operating mechanisms theoretically could be used for such upgrades. However, each of the foregoing operating mechanisms has inherent complexities and costs that will make the use of such operating mechanism unattractive for retrofitting.